What Does "opacity" Refer to in the Context of the Pulmonary System?

Opacity means an area of increased density on a lung X-ray, according to Radiology Assistant and the University of Virginia. This can be a sign of an abnormality or disease process.

An opacity can mean a consolidation. This means that the alveoli, or the tiny air sacs in the lungs, may be full of blood, pus or fluid. They could also be full of cancerous or noncancerous cells or other materials, according to Radiology Assistant. Consolidation is often a sign of pneumonia. The condition spreads from one alveolus to another but stops when it reaches a fissure in the lung. Consolidation can be acute or chronic.

It is also possible to see if the structures that support the lung tissue itself contain nodules or opacities with a netlike or reticular appearance, says Radiology Assistant. One reason for this is that a reticular pattern is easier to see on an X-ray. Other patterns are ground glass and cystic patterns, but they are difficult to make out on an X-ray. Another type of opacity seen on a lung X-ray is a nodule or some kind of mass. These nodules or masses can appear anywhere in the pulmonary system. They can be singular or come in groups.

Another opacity type can signal that a part of the lung has collapsed because of problems with the alveoli, claims Radiology Assistant.